This invention is directed to superabsorbent materials that can withstand mechanical forces without a significant reduction in absorbency properties, specifically gel bed permeability and/or average particle size. This invention is also directed to methods of increasing the damage resistance of superabsorbent materials.
Commercial superabsorbent materials are widely used in a variety of personal care products, such as infant diapers, child training pants, adult incontinence products, feminine care products, and the like. These superabsorbent materials, or hydrogels, are essentially crosslinked polyelectrolytes, which are water-swellable, water-insoluble and exhibit very high water absorbency. In general, these crosslinked polyelectrolytes have a centrifuge retention capacity (CRC) of at least 15 grams of 0.9 weight percent sodium chloride aqueous solution per gram of the polymer. Superabsorbent materials are also designed to quickly uptake bodily fluids, which requires that the superabsorbent materials have high gel bed permeability (GBP). Commercial superabsorbent materials undergo significant particle damage during manufacturing and converting processes, resulting in great loss of their original gel bed permeability. This reduction in the original gel bed permeability may be one of the causes of premature leakage and skin wetness problems.
These superabsorbent materials are characterized as glassy polymers and are very brittle under mechanical impact and stress when they are dry or at a low relative humidity (RH) environment, such as a RH below 30%. Due to their glassy and brittle nature, these polymers suffer a significant breakdown in particle size and shape during manufacturing processes, such as diaper manufacturing processes. Major mechanical damage of the polymers occurs from high-speed impact in air conveying and mixing steps and high-pressure compression in product densification steps. This particle damage is further increased in products employing high superabsorbent material content as product manufacturers strive for thinner products. This mechanically-induced damage to the superabsorbent materials reduces the effectiveness of the materials, also illustrated in the Examples herein.
There is thus a need or desire for a superabsorbent material that can withstand absorbent product manufacturing and converting processes without resulting in a significant reduction in absorbent properties, specifically gel bed permeability and/or particle size. There is a further need or desire for a method of increasing the damage resistance of a superabsorbent material.